All Contact types have the following tabs in common: Todos, Files and Supplier Details.
Whereas Todos and Files are used for all Contact types, Supplier Details are usually only used for Global Contacts, since they can provide Rental Equipment or other Equipment that is needed.
Assign a User a Todo from a specific Contact, e.g. to remind him to call this person. Custom Todo's are created in Server Setup > Contacts tab > History Actions List. Refer to the Server Setup manual for more details.To create a new Todo, click on the green plus icon. Select the header, date and link it to a Project. This Todo will only have the visual link to the Project, it won't appear in the Project view.
Contact-related files can be uploaded here. Use the icons in there to (in order): Go Back, create a New Folder, Cut, Paste, Copy, Rename, Delete, Upload, Download. Sort the files by name or by date.
Contacts can act as an External Supplier that provide external Objects belonging to existing Object Classes. Click on the green plus icon and select those Object Classes that this Contact supplies. Double click on the Object Class line, that just got added and fill in the fields as needed: add a Reference, Buy and Sell prices and set the Rate to be day-based or hour-based. This option works in combination with the setting in the Toolbox settings tab > Class/Objects: Auto Book External Object When No Object Found. See Toolbox > Settings tab > Class/Objects.